Piezoelectric crystal body comprised of rubidium compound



June 8, 1954 H. JAFFE 9 3 PIEZOELECTRIC CRYSTAL BODY COMPRISED OFRUBIDIUM COMPOUND Original Filed June 8, 1944 CRYSTALS Emmet) o: Pmmm;Roalolum ARQENATE, On MmCzvsn-AL, RIMARY 2 Rusiolum PHOEIVHATE AN PmmgcwAmmonium PHOSPHATE INVENTOR. HANS JAFFE ATTOR N EY Patented June 8, 1954PIEZOELECTRIC CRYSTAL BODY COM- PRISED OF RUBIDIUM COMPOUND Hans Jafie,Gleveland, Ohio, assignor, by mesne assignments, to Olevite Corporation,Cleveland, Ohio, a corporation of Ohio Original application June 8,1944, Serial No. 539,312. Divided and this application May 18, 1948,Serial No. 27,663

2 Claims. 1

This invention pertains to a piezoelectric crystal element cut withparticular orientation from any one of a number of representatives of afamily of crystals.

This application is a division of copending application filed June 8,1944, in the name of Hans Jafle, Serial Number 539,312, forPiezoelectric Crystal Means, now Patent No. 2,463,109.

The present application pertains to a piezoelectric crystal body outwith particular orientation from a P-type mother crystal of tetragonalsymmetry comprised at least in part of material selected from the groupprimary rubidium, cesium or thallium phosphate, and primary rubidium,cesium or thallium arsenate.

The term P-type crystal is to be understood as embracing the tetragonalcrystal form of primary ammonium phosphate (NH4I-I2PO4), primarypotassium phosphate, primary rubidium phos phate, the primary arsenatesof ammonium, potassium, and rubidium, isomorphous mixtures of any ofthese named compounds among each other and with primary thalliumphosphate, and all other piezoelectrically active crystalline materialsisomorphous therewith. In Wyckoif, Structure of Crystal (2nd edition, N.Y. 1931) this crystal type is introduced as KHzPOt-type. In theStrukturbericht (supplement to Zeitschrift fuer Kristallographie) thistype here introduced as P-type designated as type 31-2-2.

A further object of my invention is to provide a plate of piezoelectriccrystalline material useful in a transducer and which is not as limitedin its uses by temperature conditions as plates of Rochelle saltcrystalline material.

Another object of my invention is to provide a piezoelectric transducerelement having a satisfactory coupling coefficient.

A further object of my invention is to provide new piezoelectriccrystalline materials and new elements cut therefrom.

Still another object of my invention is to provide improved syntheticpiezoelectric elements for filter circuits.

A further object of my invention is to provide cuts of piezoelectriccrystalline material which exhibit an electro-optic effect to a markeddegree.

It is also an object of my invention to provide means for and a methodof light intensity and color modulations utilizing a piezoelectriccrystal element.

For a better understanding of the present in vention, together withother and further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

Fig. l is an isometric view of a mother crystal with crystal bodies cuttherefrom in accordance with the invention, and Fig. 2 is an isometricview of a mother crystal after it has been partially processed in orderto obtain another crystal body.

In an embodiment of the invention, there is provided, as an article ofmanufacture, a piezoelectric crystal body out from a crystal oftetragonal symmetry comprised at least in part of material selected fromthe group primary rubidium phosphate, primary cesium phosphate, primarythallium phosphate, primary rubidium arsenate, pri mary cesium arsenateand primary thallium arsenate; and the body has a pair of substantiallyparallel clectrodable surfaces substantially perpendicular to the Z axisof the crystal material.

In the parent application Serial Number 589,312 (now Patent No.2,463,109) there is described and claimed a crystal body comprised,aside from any impurities, of primary ammonium phosphate. I have furtherfound that useful piezoelectric elements are obtained from crystalsgrown from a solution which contains, in addition to primary ammoniumphosphate, such other chemicals as the primary phosphates of potassium,rubidium, cesium, or thallium, and the primary arsenates of these samemetals. Crystals grown from a solution containing primary ammoniumphosphate and one or more of the quoted chemicals are found to bemix-crystals, or solid solutions, containing considerable amounts of theadded phosphates or arsenates.

About the crystal substance primary rubidium phosphate there arecontained in the literature only few and contradictory statements on thecrystal system to which it belonged; one author, Berg (Berichte DeutscheChemische Gesellschaft, vol. 34, p. 4182, 1961), stating that itcrystallized in quadratic prisms; another author, West (Zeitschrift f.Kristallographie, vol. 74, p. 306, 1930), stating that it was opticallybiaxial and hence of a diiferent symmetry from primary ammoniumphosphate. I have discovered that actually primary rubidium phosphatemay crystalliae in one of two entirely different crystal types, one ofwhich is piezoelectric. The non-piezoelectric type crystallizes uponrapid cooling of a concentrated solution; it is optically biaxial andbelongs to the monoclinic system. No trace of piezoelectricity could befound with this crystal by the click test. The piezoelectric type ofcrystal which I usually obtained upon slow cooling or by evaporation ofsolutions near room temperature is of tetragonal symmetry and in habitclosely resembles primary ammonium phosphate. The crystal is opticallystrictly uniaxial and its birefringence is about half that of primary ammonium phosphate. The crystal is stable over long periods of time; uponheating, it is found to be subject to a transition somewhat above 70 C.,which will result in destruction of the crystal. The type ofpiezoelectric effects which I obtained on this substance show definitelythat the symmetry of the substance is the same as that or primary ammc1m phosphate.

By experimenting with mixed aqueous solutions of primary ammoniumphosphate and primary rubidium hosphate, for instance, in the ratios 1:1and I have ascertained that there exists an unbroken series ofmix-crystals of primary ammonium phosphate and primary rubidiumphosphate. Crystals grown from the solution containing the components inmolar ratio 1: contained .85 mole of primary ammonium phosphate per oneinc-l of primary in idium phosphate. The piezoelectric constant cise formix-crystals of this composition was found to be substantially the samefor pure- 3: lary rubidium phosphate. l lo ever, such mix-crystals havethe advantage that the transition point mentioned before for the case ofpure primary rubidium phosphate is shifted to higher temperatures. Forthe mix-crystals of the aforementioned composition it is found not to bebelow 145 C.

I have found that crystals of primary ammo nium phosphate grown from anaqueous solution of this salt and varying amounts of primary cesium phosto do contain certain amounts of cesium. Solutions containing cesium upto the molar ratio Cs to Nil-1:11 can be employed advantageously. Withcesium contents substantially in excess of this ratio, deposition ofmonoclinic primary cesium phosphate crystals is observed; the latter Ifound not to be piezoelectric. 6n the other hand the aforesdescri-bedammonium phosphate crystals containing certain amounts of cesium havebeen found to have a piezoelectric coeihcient (Z36 about equal to andpossibly higher than the corresponding constant for pure primaryammonium phosphate.

I have also studied primary thallium phosphate and the mix-crystalsobtained from aqueous solutions containing both primary ammoniumphosphate primary thallium phosphate, and found the monoclinic crystalsof primary thallium phosphate not to be piezoelectric. Markedpiezoelectric effects are obtained however from the tetragonal crystalsobtained from solutions containing primary ammonium phosphate andprimary thallium phosphate up to a molar ratio thallium to ammoniumabout 1.5 to 1. It is known by the work of Rammelsberg published in(Sltzungsberichte Akad. Wiss. Berlin and quoted in P. Groth, ChemischeKristallogn, vol. 2, p. 794) that tetragonal mix crystals containing upto 33 mol per cent of primary thallium phosphate grow in such solutions.The crystals obtained from aqueous solution containing ammonium andthallium in substantially equal molar amounts show a piezoelectriccompliance coefilcient clil lO X10" meter/volt or some 30 times as highas the corresponding constant for pure ammonium phosphate. The constant(13s for this mix-crystal was found to be of similar magnitude as forpure ammonium phosphate. The optic birefring nce of this mix-crystal isonly about onehalf that of pure ammonium phosphate, which fact is ofadvantage in electro-optic applications Where a beam of considerableangular aperture is to be modulated.

Figure 1 shows a mother crystal In comprised of any of the materialsheretofore mentioned, and indicates the X, Y and Z crystallographicaxes.

The plate I l which may be cut from the mother crystal It is called aZ-cut plate because the major parallel electrodable faces aresubstantially perpendicular to the Z axis.

The plate i2 which may be out from the mother crystal ID is called anX-cut plate because the major parallel electrodable faces aresubstantially perpendicular to the direction of extension of the X axis.lhis plate may also be called a Y cut because in crystals of this typethe X and Y axes are equivalent to each other.

Figure 2 illustrates a bar l5 having faces cut at 45 degrees to thenatural edge faces of a mother crystal in accordance with thisinvention. A plate or body :3 may be cut from the bar l5 in such adirection that a line normal to the major faces of the plate makessubstantially equal angles with the X, Y and Z crystallographic axes.This plate l3 may be called a thickness expander plate because itexpands and contracts in its thickness direction when an alternatingfield is impressed thereon in a direction parallel to the thicknessdimension.

The aforementioned plates are of particular value Where the plate is cutfrom a mother crystal containing a substantial amount of thallium.

Each of the aforedescribed plates is adapted to have an electrodeapplied to its major faces, as i known to the art.

While there have been described what are at present considered to be thepreferred embodimerits of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

I claim:

1. As an article of manufacture, a tetragonal piezoelectric crystal bodycomprised of primary rubidium arsenate.

2. an article of manufacture, a tetragonal piezoelectric mix-crystalbody comprised of pri mary rubidium phosphate and primary ammoniumphosphate.

References Gited in the file of this patent UNITED STATES PATENTS NumberName Date 2,373,445 Baerwald Apr. 10, 1945 2,44%590 Bokeny July 6, 19482,48%,635 Mason Oct. 11, 1949 OTHER REFERENCES Electrostatic andPyroelectric Phenomena, by W. G. Cady, published in vol. 6, 1929,International Critical Tables, pages 207-212.

Hopkins, Chemistry of the Rare Elements, C. D. Heath 8; Cd, N. 1., 1924,page 51.

Hoffman, Lexikon der Anorganischen Verbindungen, Band 1, l. I-lalfte, liasserstofi bis Silber, No. 1-31, Barth, Leipzig, 1917, page 347.

Bartschi et al., Helv Phys Acta 18 (1945), pages 240-2, CA vol. 40, page9 (1946).

1. AS AN ARTICLE OF MANUFACTURE, A TETRAGONAL PIEZOELECTRIC CRYSTAL BODYCOMPRISED OF PRIMARY RUBIDIUM ARSENATE.